June 21, 2022
By Karen Maxwell, Horticultural Specialist
On a recent evening, just after sunset, as the crepuscular creatures were venturing out, I walked into the Moonlight Garden to turn off lights that had been left on for a special event. Strolling around, my mind was wandering, contemplating various subjects for this month’s article when I was seduced by an intoxicating fragrance that filled the soft dusky air.
In our Moonlight Garden, there are no less than six varieties of gardenias—one actually belongs to the Tribe Gardenia, meaning it is not a true gardenia by botanical definition, but more on that later. Gardenias are included in the plant family Rubiaceae, which also includes coffee, pentas and quinine.
Taxonomically speaking, the common gardenia is Gardenia jasminoides where the species epithet means jasmine like. In some literature, Gardenia jasminoides is synonymous with Gardenia florida (meaning many flowers) and Gardenia augusta. The genus name honors Alexander Garden (1730-1791) who was a Scottish physician, a naturalist, a resident of Charleston, South Carolina and a correspondent of Linnaeus, the father of botanical classification. Commonly, gardenias are also referred to as Cape Jasmine in some parts of the world.
Most species of gardenias originated in the eastern hemisphere. As early as the Song Dynasty (960-1279 AD), the Chinese were cultivating gardenias, which made their way to South Africa and on to England as early as 1760, and shortly thereafter arrived on the shores of the soon-to-be United States. Since then, nothing speaks of Southern charm and culture in flowers as does the gardenia.
My Florida horticulture hero, Henry Nehrling (who was employed by the Edisons in Fort Myers in 1928), wrote in 1925, “Camellia, rose and gardenia were the most fashionable flowers of the antebellum days … the glorious fragrance [of the gardenia] … and pure white color— another point in its favor …”
The architect who designed Edison’s Study and the Pool Complex, Hal Walker, also designed a Flower Garden for Mrs. Edison in 1928 for the areas between the houses and outside of the pergola that included gardenias. Historic inventories list G. augusta, specifically August Beauty on site during the years 1930-1936.
The fragrance is why most people want to grow gardenias. With more than 200 varieties ranging from dwarfs that grow only two feet tall, to gardenia standards (small trees) reaching to 12 feet, such as those that anchor both ends of the eastern path through the Moonlight Garden, we will share the formula for success in a Southwest Florida garden.
Gardenia flowers are waxy and they all open as a white flower – some a bright white, while others have flowers that fade to off white or pale yellow or orange. Yes, orange. Gardenia flowers may be single or double, clustered or solitary. All are fragrant. These are slow-growing plants with a lifespan of approximately 20 years.
In Southwest Florida, the most popular variety is Miami Supreme, followed by Aimee, which offers larger, but later blooms. Gardenias are susceptible to the root-knot nematodes in our sandy soils, so the University of Florida recommends purchasing a gardenia that has been grafted onto Gardenia thunbergia rootstock, resulting in a more vigorous gardenia shrub. The limiting factor of these grafted gardenias is that they are not cold-hardy and will die if the temperature drops below 28 degrees. Un-grafted gardenias can grow as far north as zone 7b. Such is our lot as a Southwest Florida gardener – but when one considers that we have managed to survive without the ability to grow camellias, we should be happy we have the opportunity to grow lovely gardenias. (For those left wondering, Gardenia thunbergia is native to Zimbabwe, where it is known as the wild gardenia and it is used by the Karanga of Zimbabwe to ward off witchcraft. It has an intense, almost over-powering scent.)
A historical postscript: A noted colleague, friend and neighbor of the Edisons, James Hendry who owned and operated the Everglades Nursery, which was located just up the road on McGregor Boulevard, is credited with being the first nurseryman to graft Gardenia veitchi with Gardenia thunbergia and according to a News-Press article dated May 5, 1975, was the granddaddy of our grafted gardenias.
Gardenia lovers are encouraged to limit their garden to one or two plants as these shrubs are as attractive to insects as they are to humans. For this particular reason, while they do grow well in pots, we don’t recommend them as houseplants. Gardenias attract scales, thrips, aphids, and whiteflies, which can be managed outside with regular applications of horticultural oils or Neem as directed on the packaging. Should you observe sooty mold (a black powdery-like substance) on gardenia leaves, closer inspection will most likely reveal ants marching up and down its stems. They are after the honeydew of the insects and it is a call to action. During times of extended dry periods is when this would typically occur.
Gardenias thrive in well-drained organic, acidic soils, with a pH range of 5.0-6.5, similar to the preference of azaleas and camellias. Most of our Southwest Florida soils tend to be alkaline (higher than 7.0) so we must make a few adjustments to keep our gardenias in top form.
Begin by planting the gardenia in a mound, higher than the surrounding garden area, and be sure to keep the flare (where the bottom of the trunk meets the roots or graft) above the soil line. Keep an eye on this after the first year, as often they will sink as the disturbed soil settles during the rainy season. This is good advice for planting most trees, by the way. Most importantly, plant your gardenia where you will be able to enjoy its fragrance and, like roses, they appreciate very good air circulation. Gardenias will thrive with some afternoon shade during the heat of summer, but they can endure full sun with appropriate watering. They are not at all salt tolerant and will show their disdain if briny reclaimed water, or household softened water is applied. Be sure to keep them moist and apply a nice four-inch layer of good organic mulch over their roots.
Maintain a good feeding regime of a quality fertilizer with minors (the other trace elements of a complete fertilizer) formulated for acid-loving plants, two to three times a year – February and October and if the leaves are showing signs of deficiency, also feed in June and again in August. Our alkaline soils block acid loving plants from accessing iron, magnesium and nitrogen from the soil. The tell-tale signs of these deficiencies are as follows: If the leaves have yellowing between the veins, it is iron deficient; if the leaves are yellowing from the outer margins inward, the plant is magnesium deficient; if all of the leaves are yellowing, it is nitrogen deficient. Purchase fertilizer for acid-loving plants – the fertilizer should be complete and include ammonium sulfate, ammonium nitrate, iron sulfate and sulphur-coated urea.
In the absence of the correct fertilizer, the gardener can add dry coffee grounds to the soil or one tablespoon of Epsom Salts mixed with one gallon of water, once a month; or apply one tablespoon of vinegar to one gallon of water, once every three months.
When to prune is a common question. Give only a minimal pruning to maintain desired shape and vigor after the plant has completed its blooming cycle. If pruning is done after October 1, the number of blooms the following spring will be greatly diminished. Should bud drop start to occur, it could be from natural causes such as an extended dry and hot spell, or very cool weather. Inadequate drainage or too much fertilizer will also lead to the loss of buds.
In addition to Gardenia jasminoides, visitors to our Moonlight Garden can also view several other varieties, including Gardenia nitida native to West Central Africa. It is a shrub that can grow to twelve feet. The single flowers have long tubular throats for pollination by hawk moths. G. nitida is unusual in that it will develop lots of flowers in one day, and they are all gone the next. It will repeat this bloom pattern several times a year. Gardenia nitida was first identified by William J. Hooker, the first director of Kew Gardens in England.
As one enters the Moonlight Garden from the northwest (and original) entrance, there is Gardenia taitensis, Heaven Scent on the left (they also flank the riverside entrance to Ford’s cottage.) Neither native to nor naturalized in Tahiti, the name is misleading. However, it is now the national flower of French Polynesia and the Cook Islands. It grows up to eight feet with glossy, deep green leaves. The flowers are used to make perfume oil by infusing them in coconut oil.
Speaking of misnomers, the Vietnamese Gardenia is neither from Vietnam, nor a true gardenia in that its seed pod has grooves, unlike true gardenias, but botanists do classify this Kailarsenia in the tribe gardenia. This closely related plant otherwise looks and smells like a single flower gardenia and it tolerates very moist soils, is highly resistant to root-knot nematodes and is free flowering all year. It is most fragrant in the early evening.
With a flower structure similar to G. nitida, don’t miss Gardenia tubifera, or Golden Gardenia, which is located along the pathway to the Caretaker’s Cottage along the eastern side of the Moonlight Garden – it is tucked in between the Tabernaemontanas – which are often mistaken for gardenias. An easy way to tell the difference is the lack of strong fragrance, and all of the Tabernaemontana have milky latex oozing from their stems. To add to the confusion, these gardenia look-a-likes are often referred to as Crepe (or Crape) Jasmines, while Cape Jasmine is a common name for gardenias. So, the next time you visit the Moonlight Garden, please stop to smell the gardenias!